1. Field of the Invention
The present invention generally relates to the field of mechanical locking and positioning devices and more particularly concerns mechanical locks of the type where a rod is axially translatable through a lock housing, a clutch spring is axially fixed to the lock housing and normally grips the rod against axial displacement through the lock housing, and a release lever is actuatable for unwinding the spring to release the rod.
2. Background of the Invention
Mechanical locks of this type are known and have been used, especially in adjustable automotive seats. Typically, one or more mechanical locks control elevation and tilt angle of the seat, and also lock the seat on horizontal rails so that the seat can be positioned at a preferred distance from a steering wheel or dash panel. One example of such a lock is disclosed in U.S. Pat. No. 3,874,480 issued to Porter et al. and owned by the Assignee of this patent application. One end of the coil spring has an end tang which is circumferentially fixed to the lock housing. By actuating a release lever acting on an opposite free end of the coil spring, the coil spring is unwound sufficiently to enlarge its inside diameter and release the rod. Such locks typically include axial bearing surfaces which operate to angle or cant one or more end coils of the spring in response to axial loading of the rod relative to the lock housing.
In applications where bi-directional loading of the rod is anticipated, two springs may be provided, one on each side of a common release lever and axially contained between two end bushings, each bushing engaging an end tang of a corresponding spring to fix the tang and the outer end coils of the spring against rotation about the rod. The inner end coils of the springs are connected to a release lever, actuatable for simultaneously unwinding both springs to free the rod for axial movement through the housing.
The bushings serve three distinct functions. An axial bore in each bushing defines a radial bearing surface which supports the rod for sliding movement through the lock housing. A radial slot in the bushing receives an end tang of the spring, to circumferentially fix the outer end of the spring and prevent this end of the spring from turning about the rod. Finally, an axial bearing surface on the bushing is circumferentially spaced by 90 degrees from the spring tang. When the spring is pulled with the rod against the axial bearing surface by a load acting on the rod relative to the lock housing, the end coils of the spring are canted relative to the rod axis. This canting of the coil springs deforms the coils from a normal circular shape to an ellipsoid shape, and substantially increases the frictional engagement between the spring coils and the rod. The clutch spring better resists the load and makes for a more positive lock of the rod relative to the housing so long as the loading condition persists.
Prior art locks also feature a tubular sleeve which closely envelops the spring or springs, to prevent the coils from unwinding preferentially at the release lever while the coils at the opposite end remain in a rod griping condition. The sleeve prevents this result by distributing the unwinding action more evenly along the length of the spring so that all coils release the rod at substantially the same time, for positive, quick release action of the lock.
Early locks of this type were housed in a cylindrical tube open at one or both ends. The clutch spring was mounted on the rod, and other components such as end bushings, actuator levers, etc. all assembled onto the rod and then inserted into the housing. The housing wall was then swaged or welded to hold the internal components in axially fixed position within the housing. The relative positions of the lock elements in the housing is rather critical and a high degree of precision must be maintained in assembling the lock. A tube type housing makes this objective difficult to achieve with consistency.
More recently, the tube style housing has been replaced by a two-piece clam shell housing. This approach is described in European patent application number 85201888.6 filed Nov. 18, 1985, Publication number 0 182 440 83. An envelope or housing is formed by two half shelves made of stamped plate and separate from one another. The rod is first fitted with the coil spring, release lever, and a pair of end bushings which engage the ends of the coil spring. The device is assembled by mating the half shell to each other with the rod in between, then welding the half shells to the bushings to form an enclosure about the rod. The axial spacing between the bushings is fixed by this welding, thus fixing the spring between the bushings. The rod slides through the bushings and the housing when the spring is unwound to permit such movement.
Assembly of the two half-shells to make the lock housing still entails a number of difficulties. Two separate stamping dies are required to make the two half shells. Two separate pieces must be handled and must be brought into and held in positive axial registry while they are welded to the bushings to keep the unit within proper working tolerances.
For these and other reasons, further improvement is desirable in linear mechanical locks of this type, to simplify and improve the accuracy of the assembly, and to reduce the parts count of the lock.